MAR Pathogen13 of the month – Mar 13 Fig. Symptoms of orange stromata containing fruiting bodies of C. parasitica; stromata associated with a trunk wound; trunk cankers with swelling and cracking (images courtesy of David Smith, DPI Victoria) Disease: Chestnut blight, chestnut canker; Causal agent: Cryphonectria parasitica Classification: K: Fungi, P: Ascomycota C: Sordariomycetes, O: Diaporthales F: Cryphonectriaceae Chestnut blight is a serious fungal disease of chestnut (Castanea spp) caused by Cryphonectria parasitica. The pathogen is a wound parasite originating in Asia which caused severe epidemics in endemic populations of American and European chestnuts in North America and Europe, respectively. The pathogen can cause cankers, blighting and tree death and is readily spread via trade in infected (Murrill) Barr (Murrill) chestnut propagating material and other host tissue. An outbreak of the disease in north-east Victoria, Australia is the subject of a national eradication response which began in 2010. Biology and Ecology: Splashed conidia and Disease Impact: The accidental introduction of wind blown ascospores can infect wounds in the C. parasitica into North America in the late bark of trees. Cankers form and may girdle nineteenth century initiated a major ecological branches causing blighting of shoots above the disaster in forests in eastern USA, reducing an infection. Orange-red stromata form on cankers estimated 3.5 billion American chestnuts (C. and produce pycnidia and, less often, dentata) from a dominant forest tree to a minor perithecia. understory component. In Europe the impact on The pathogen can survive and sporulate on planted and forest chestnuts (C. sativa) although dead wood for 1-2 years, and although roots serious was less significant. This is possibly due appear to be resistant, some reports indicate to C. sativa being slightly more resistant than C. survival on the underground stumps of infected dentata, and also due to the presence of trees. hypovirulent strains of the pathogen which can induce healing of cankers caused by virulent Disease is favoured by a humid temperate strains. Asian species of chestnut are less climate, whereas dry conditions slow its affected although disease can be severe even in development and spread. these trees. Under favourable conditions, tree Distribution: The disease was first reported death of susceptible species can occur within from North America in 1904 and Europe in four years. The pathogen can kill some oak 1938, but originated in eastern Asia. species, but generally oaks are less susceptible Australasia, South America, most of Africa and than chestnuts. parts of northern Europe are still free of this Disease Management: Quarantine, use of pathogen. hypovirulence as a biocontrol, resistance breeding, and eradication are all useful Host Range: Chestnut and oak are the major management practices. Fungicides are generally hosts, although a number of other unconfirmed ineffective against this disease. hosts have been reported. Cryphonectria parasitica parasitica Cryphonectria Further Reading: Anagnostakis (2000) APSnet features online. Gryzenhaut et al (2009) APS Press. Liberato and Robin (2006) PaDIL (online). Key contacts: Bill Washington, BV, DPI Victoria, e-mail: [email protected] Jacky Edwards, AgriBio, DPI Victoria, e-mail: [email protected] .